Effect of pH, temperature and some chemicals on polyphenoloxidase and peroxidase activities in harvested Deglet Nour and Ghars dates

• Optimal temperatures for PPO activity in Deglet Nour and Ghars dates are 35 and 40 °C.
• Optimal pHs for POD activity in Deglet Nour and Ghars dates are 5.6 and 6.4.
• PPO and POD from both varieties remain active in broad pH and temperature ranges.
• Ascorbic acid is a potent inhibitor of PPO and POD activities in both varieties.
• The POD activity of both varieties is strongly inhibited by EDTA and SDS.

The influence of pH, temperature and some chemicals on polyphenoloxidase and peroxidase activities in harvested Deglet Nour and Ghars dates was studied. These activities were tested for optimum pH and temperatures. Their stability was assessed as a percentage of remaining activity after incubation at different pH and temperatures and in the presence of some chemicals. The determination of phenol content and antiradical activity of fruit extracts in the presence of these chemicals was also carried out. Optimal pHs and temperatures for polyphenoloxidase activity in Deglet Nour and Ghars are pH of 6.4 and 7.2 with temperatures of 35 °C and 40 °C respectively. For peroxidases the conditions are 5.6, 6.2 and 35 °C, 30 °C respectively. The most inhibitory chemicals to both enzymes were ascorbic acid, sodium metabisulfite and cysteine. The highest phenol content of both varieties is in the presence of sodium metabisulfite. The highest anti-radical activity is that in the presence of ascorbic acid. Deglet Nour and Ghars enzymatic browning can be completely inhibited by some chemicals and extreme pH and temperatures.

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